The present invention relates to a solid-state image sensor which has a high resolution and a high signal-to-noise (S/N) ratio and can substantially avoid blooming and smear as well.
One of the most important requirements for solid-state image sensors is a high resolution so that it is preferable that the number of picture elements is increased as much as possible. Therefore, MOS-LSI techniques have been, in general, used because a higher degree of integration can be obtained in a relatively simple manner and an image unit, a shift register unit and a unit for coupling between them can be formed in a unitary construction.
In general, the solid-state image sensors can be divided into MOS type and CCD type. However, in practice, neither of these types can attain a satisfactory degree of high resolution and S/N ratio.
As will be described in detail below, in order to overcome the above and other problems encountered in the prior art MOS and CCD type solid-state image sensors, the inventors proposed in U.S. patent application Ser. No. 197,026, filed Oct. 15, 1980 a solid-state image sensor of the type comprising a plurality of photoelectric transducer elements arranged in an (m.times.n) matrix array; a charge transfer means comprising a light signal charge transfer means comprising a MOS vertical shift register and switching elements for simultaneously transferring the light signal charge stored in one column of photoelectric transducer elements to a vertical transmission line, transfer gates for transferring the light signal charge on the vertical transmission line to a horizontal shift register and storage capacitor elements; and a signal output stage for deriving light signal charge which has been horizontally transferred through the horizontal shift register which comprises a CCD type horizontal shift register.
The solid-state image sensor with the above-described construction can attain a high resolution and a high S/N ratio hitherto unattainable by the prior art solid-state image sensors, but still has much to be improved; that is, the resistance to blooming or capability of avoiding blooming. Blooming occurs when the charge generated by the incident light is in excess of the maximum charge storage capacity of a photoelectric transducer element. As described in the above U.S. patent application Ser. No. 197,026, even though the resistance to blooming or the anti-blooming characteristic is improved, when a spot of light (about 10% of the vertical direction of the whole area of the picture elements) is incident, the blooming charge reaches tens of times that generated when the light quantity is saturated. Therefore, in order to provide a solid-state image sensor which is satisfactory in practice, the resistance to blooming or the anti-blooming characteristic must be further improved.
In order to avoid blooming in the prior art MOS or CCD type solid-state image sensor, there have been proposed various methods, but no method has been devised which can fundamentally or completely avoid blooming.